In the power supply system for electric vehicles in an urban subway system, the conductive rail traction power supply technology is often used to reduce the construction cost of line construction. The so-called “conductive rail traction power supply” is to add a charged rail, besides the two rails for train running. The charged rail is usually located between the two rails or at the outside of one rail. The collector shoes of current collecting equipment of the electric trains contact with and slide on the charged conductive rail, so as to transmit the electric power to the train.
At present, all existing conductive rails are steel-aluminum compound rails, and single conductive rail usually has a length of 12-20 meters. Therefore, a plurality of conductive rails must be connected with each other electrically and mechanically, in order to provide electric energy for the electric train. Like all rails, conductive rails expand with heat and contract with cold with following temperature change. Therefore, appropriate clearance must be arranged between the ends of two adjacent conductive rails. To achieve electric connection between two adjacent conductive rails, a telescopic conductive joint must be installed at the joint of the two conductive rails when laying conductive rails, and the conductive joint must have low contact resistance, high reliability, and be easy to install, etc.
In the past, conductive rails are electrically connected to each other through the connection of fish plates at both ends of the conductive rail. To improve reliability of the electric connection, an expansion joint is added at the joint of the conductive rails nowadays.
In the prior patent application No. CN200720036403.7, “Conductive Rail Compensation Apparatus for Rail Transit”, an expansion joint composed of three silver-plated copper plates (primary and secondary plates) that can slide relatively to each other is disclosed. The primary and secondary plates of the expansion joint are fixed to the conductive rails, with the primary plate being inserted between the two secondary plates, and these plates are fixed with a U-bolt fixture with a backing plate. Springs are arranged on the U-bolts, and the primary and secondary plates achieve conducting function by planar frictional contact. However, such an expansion joint has some drawbacks in actual application, mainly including: the contact resistance between primary plate and secondary plate is not easy to control, that is to say, the vibrations and change of local temperature generated during train operation, abrasion and erosion of primary and secondary plates, intrusion of foreign matters, and change of clamping force, etc., will result in change of the contact resistance; (2) the bolt torque is difficult to control: if the bolt torque is too large, the pressing force between primary and secondary plates will be too large, and therefore the expansion joint can't expand and contract smoothly, thus during deformation of expansion or contraction of the conductive rail, large resistance force will be generated which may even result in deformation of the conductive rail; if the pressing force is not large enough, the primary and secondary plates can not get in good contact with each other, and therefore the contact resistance will increase and result in adverse effect to current-carrying; (3) due to the fact that some voltage drop exists at the contact point or contact surface between the primary and secondary plates, phenomena such as overheat or arc ablation may occur when the contact resistance is too large or the contact is not good. In the prior patent with No. ZL02820582.0, “Telescopic Connector for Conductive Rails), a telescoping connector that employs a multi-layer metal conductor is disclosed. In the embodiments, flexible connection of multi-layer metal straps with superior electric conductivity is mainly used. The electric conductive metal strap is fixed to connection elements, which are made of non-metal materials, and can be mounted in or on the opposite ends of contact rails (conductive rails) in a movable or slideable manner, to ensure the conductive rails only expand and contract along the length direction. However, when the conductive rails expand or contract in the longitudinal direction, it is difficult to maintain balance of frictional resistance forces in the sliding grooves on both ends of the connecting elements. In addition, the multi-layer metal strap has a certain degree of rigidity. Therefore, when the contact rails expand or contract, it is difficult to ensure a uniform and even compression or extension journey for the curved parts on the two sides, for example, the expansion/contraction range on one side may obviously asymmetric to that on the other side, or the curved part on the side of the electric conductor is excessively compressed or extended repeatedly, resulting in fatigue damage or even fracture of parts of the metal straps. In extreme cases, for example, only the curved part on the side of the conductive body expands or contracts and results in excessive elastic deformation of the curved part, the conductive body may further come into contact with the ground or the bottom of conductive rail, causing a potential safety hazard or safety accident.